EP2174861A1

EP2174861A1 - Seat frame and saddle-riding type transporter including the same

Info

Publication number: EP2174861A1
Application number: EP09012764A
Authority: EP
Inventors: Takaharu Suzuki; Shuji Tominaga; Kenji Tsukamoto
Original assignee: Yamaha Motor Co Ltd
Current assignee: Yamaha Motor Co Ltd
Priority date: 2008-10-09
Filing date: 2009-10-08
Publication date: 2010-04-14
Anticipated expiration: 2029-10-08
Also published as: EP2174861B1; JP2010111384A; JP5386291B2

Abstract

The generation of a casting defect is suppressed which would otherwise occur to frame members of a seat frame when being formed of a magnesium alloy or an aluminum alloy by casting. The seat frame (100) according to the present invention is for a saddle-riding type transporter (200), and includes a pair of frame members (10L,10R) formed of a magnesium alloy or an aluminum alloy by casting. The pair of frame members (10L,10R) each include a first side wall (11), a second side wall (12) located outer with respect to the first side wall (11) in a vehicle width direction (B), and a connecting wall (13) for connecting the first side wall (11) and the second side wall (12) to each other. The connecting wall (13) includes seat fixing section (13a,13b,13c) for fixing a seat (136,139). The pair of frame members (10L,10R) each include a first region (R1) in which a top end of the first side wall (11) and a top end of the second side wall (12) are connected to each other by the connecting wall (13), and a second region (R2) in which a portion below the top end of the first side wall (11) and a portion below the top end of the second side wall (12) are connected to each other by the connecting wall (13). The seat fixing section (13a,13b,13c) is located in the first region (R1).

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to a seat frame, and in particular to a seat frame including a frame member formed of a magnesium alloy or an aluminum alloy by casting. The present invention also relates to a saddle-riding type transporter including such a seat frame.

2. Description of the Related Art:

Conventionally, steel has been used as a material of many elements of transporters such as motorized vehicles and the like because of having excellent mechanical properties and processability and costing low. Today, however, transporters need to be lightweight in order to provide improved fuel consumption and running performance. Thus, use of a material more lightweight than steel has been studied.
Recently, low-cost methods for refining titanium, aluminum, magnesium and the like having a lower specific gravity than steel and methods for producing alloys containing such metals have been developed. Technologies for improving the strength and the processability of these alloys have also been developed. Thus, it is now proposed to use alloys of titanium, aluminum and magnesium as materials of elements of transporters.
In the case of, for example, a motorcycle, it is preferable that a seat frame provided below a rider seat and a passenger seat (disclosed in, for example, Japanese Laid-Open Patent Publication No. 2006-240345 ) is formed of a magnesium alloy or an aluminum alloy. By decreasing the weight of the seat frame, the fuel consumption and the running performance of the transporters can be more improved.
Such structural elements as mentioned above can have a high strength by being integrally produced by casting such as diecasting or the like. Casting allows a structural element of even a complicated shape to be produced to have a desirable shape in one step. This can reduce the number of production steps and so reduce the time and cost of production.
However, it has been found that a seat frame of a magnesium alloy or an aluminum alloy produced by casting has the following problems.
A seat frame includes a pair of frame members each extending in a vehicle length direction. According to a known structure, each frame member includes two side walls and a top wall for connecting top ends of these side walls (i.e., having a U-shaped cross-section). A large load is applied on the top wall because a rider seat on which a rider may get astraddle and a passenger seat on which a passenger may get astraddle are attached to the top wall. A magnesium alloy and an aluminum alloy both have a lower strength per unit area than steel. For this reason, it is preferable that a frame member formed of a magnesium alloy or an aluminum alloy has a larger thickness in the top wall than in the side walls.
However, when the thickness of the top wall is made larger, the thickness is made different (or the thickness difference is increased) between the top wall and the side walls. As a result, the cooling rate at the time of casting is made different (or the difference in the cooling rate is increased) between the top wall and the side walls. Therefore, a shrinkage crack or a shrinkage porosity becomes likely to be generated at a border between the top wall and each side wall. The shrinkage crack is generated due to the shrinkage caused by the solidification of molten metal. The shrinkage porosity is generated by the same cause. The shrinkage crack and the shrinkage porosity are likely to be generated especially in a frame member formed of a magnesium alloy or an aluminum alloy. A seat frame having a casting defect such as a shrinkage crack or a shrinkage porosity may be occasionally unusable as a structural element of the motorcycle.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodiments of the present invention suppress the generation of a casting defect which would otherwise occur to the frame members of a seat frame when being formed of a magnesium alloy or an aluminum alloy by casting.
A seat frame according to the present invention is a seat frame for a saddle-riding type transporter, and comprises a pair of frame members formed of a magnesium alloy or an aluminum alloy by casting. The pair of frame members each include a first side wall, a second side wall located outer with respect to the first side wall in a vehicle width direction, and a connecting wall for connecting the first side wall and the second side wall to each other. The connecting wall includes a seat fixing section for fixing a seat. The pair of frame members each include a first region in which a top end of the first side wall and a top end of the second side wall are connected to each other by the connecting wall, and a second region in which a portion below the top end of the first side wall and a portion below the top end of the second side wall are connected to each other by the connecting wall. The seat fixing section is located in the first region.
In a preferable embodiment, the pair of frame members each further include a third region in which the top end of the first side wall and a portion below the top end of the second side wall are connected to each other by the connecting wall; and the third region is located between the first region and the second region.
In a preferable embodiment, the pair of frame members each include an attaching section in a front portion thereof for attaching the seat frame to a main frame; and the second region is located in the vicinity of the attaching section.
In a preferable embodiment, the attaching section includes a boss having a through-hole.
In a preferable embodiment, the second region extends to a position at least 50 mm away rearward from a central axis of the through-hole.
In a preferable embodiment, the central axis of the through-hole is located on an extension line of the connecting wall.
In a preferable embodiment, in the second region, a height from a top surface of the connecting wall to the top end of the first side wall and a height from the top surface of the connecting wall to the top end of the second side wall increase toward the attaching section.
In a preferable embodiment, at an end of the second region on the attaching section side, the height from the top surface of the connecting wall to the top end of the first side wall and the height from the top surface of the connecting wall to the top end of the second side wall are each 6 mm or larger.
In a preferable embodiment, the connecting wall has a hole in the vicinity of the attaching section.
In a preferable embodiment, the hole is a through-hole.
In a preferable embodiment, in the second region, a distance between the first side wall and the second side wall is 12 mm or shorter.
In a preferable embodiment, the first side wall and the second side wall each have a thickness of 2 mm or larger.
In a preferable embodiment, in the second region, the pair of frame members each include a curved portion curved with respect to a vehicle length direction.
A saddle-riding type transporter according to the present invention comprises a seat; and the seat frame having the above-described structure for supporting the seat.
In the seat frame according to the present invention, a pair of frame members formed of a magnesium alloy or an aluminum alloy by casting each include a "first region" in which the top end of the first side wall and the top end of the second side wall are connected to each other by the connecting wall, and a "second region" in which the portion below the top end of the first side wall and the portion below the top end of the second side wall are connected to each other by the connecting wall. In the first region, the top end of the first side wall and the top end of the second side wall are connected to each other by the connecting wall. Therefore, a top portion of each frame member has a U-shaped cross-section. In the second region, the portion below the top end of the first side wall and the portion below the top end of the second side wall are connected to each other by the connecting wall. Therefore, the top portion of each frame member has an H-shaped cross-section.
As described above, the frame members of the seat frame according to the present invention each include two regions having different cross-sectional structures. An H-shaped cross-section has a higher strength than a U-shaped cross-section. Therefore, as compared with the conventional seat frame in which the frame members entirely have a U-shaped cross-section, the seat frame having the second region (having an H-shaped cross-section) in a part of each frame member has a higher strength. For this reason, the connecting walls do not need to be thick, and so the thickness difference between the connecting walls and the side walls (the first side walls and the second side wall) can be smaller. This can decrease the difference in the cooling rate at the time of casting between the connecting walls and the side walls, which can suppress the generation of shrinkage cracks or shrinkage porosities.
With the H-shaped cross-section, the top end of the first side wall and the top end of the second side wall protrude more upward than the top surface of the connecting wall. Therefore, in the case where the frame members entirely have the H-shaped cross-section, it is difficult to attach a seat to the frame members. However, in the seat frame according to the present invention, the seat fixing section for fixing the seat is located in each first region (having the U-shaped cross-section). Therefore, the seat can be fixed easily. Namely, according to the present invention, the generation of casting defects can be suppressed without obstructing the fixation of the seat.
It is preferable that each of the frame members may further include a "third region" in which the top end of the first side wall and the portion below the top end of the second side wall are connected to each other by the connecting wall. In the third region, the top end of the first side wall and the portion below the top end of the second side wall are connected to each other by the connecting wall. Therefore, the top portion of each frame member has an h-shaped cross-section. In the case where such a third region is located between the first region and the second region, the first side wall and the second side wall can act as a positioning section usable for attaching the seat. This further facilitates the attachment of the seat.
Typically, the frame members each include an attaching section, in a front end portion thereof, for attaching the seat frame to the main frame. The attaching section is, for example, a boss having a through-hole. In the case where the second region (having the H-shaped cross-section) is located in the vicinity of the attaching section, pads in the vicinity of each attaching section can be made smaller. Therefore, the coolability can be improved in the vicinity of the attaching section, and the generation of casting defects can be suppressed with more certainty. Owing to the second region being located in the vicinity of the attaching section, the bending stress acting on the connecting wall when the rider sits on the seat can be smaller. Therefore, the connecting wall does not need to have an increased thickness in order to be against an excessively large bending stress. This also suppresses the generation of casting defects. When attaching the seat frame to the main frame, a torsional stress may act on the attaching section and the vicinity thereof (this occurs when, for example, attaching the seat frame by tightening). Where the torsional rigidity is too high, the stress generated at the time of attaching may become large and destroy the seat frame. However, in the case where the second region is located in the vicinity of the attaching section, the torsional rigidity in the attaching section and the vicinity thereof can be smaller, which can reduce the stress at the time of attaching.
The attaching section includes, for example, a boss having a through-hole. In order to improve the strength of the seat frame, it is preferable that the width of each frame member (distance between the first side wall and the second side wall) is wide. However, the width of the frame member cannot be infinitely wide because of the relationship with the distance between the legs of the rider when the rider sits on the seat and with the capacitance of the elements of the seat frame (the tank, etc.). In order to provide a sufficiently high strength under such constraints, it is preferable that the second region extends to a position at least 50 mm away rearward from the central axis of the through-hole. In the case where the central axis of the through-hole is on an extension line of the connecting wall, the effect of reducing the bending stress acting on the connecting wall (generated around the central axis) is high and the effect of reducing the torsional rigidity in the attaching section and the vicinity thereof is also high.
In the second region, it is preferable that a height from the top surface of the connecting wall to the top end of the first side wall and a height from the top surface of the connecting wall to the top end of the second side wall increase toward the attaching section. Namely, it is preferable that the depth of the groove made by the connecting wall, the first side wall and the second side wall continuously increases toward the attaching section. Owing to such a structure, the stress can be slowly changed between the regions having different cross-sectional structures and thus the generation of a stress-concentrated area can be prevented.
In order to further improve the bending strength in a height direction (up-down direction), it is preferable that at an end of the second region on the attaching section side, the height from the top surface of the connecting wall to the top end of the first side wall and the height from the top surface of the connecting wall to the top end of the second side wall are each 6 mm or larger.
It is preferable that the connecting wall has a hole in the vicinity of the attaching section. Owing to the hole formed in the vicinity of the attaching section, the cooling rate of the portion in the vicinity of the hole at the time of casting is increased, and so the generation of casting defects in the attaching portion and the vicinity thereof can be suppressed with more certainty. Another effect that the seat frame can be more lightweight is also provided.
It is preferable that the hole is a through-hole. In the case where the hole is a through-hole, the effect of suppressing the generation of casting defects is high. In the case where the hole is a through-hole, the hole can act as a water hole and so the corrosion resistance is improved. Furthermore, the generation of an air pocket is prevented at the time of undercoating or electrodeposition coating. This provides an effect of improving the throwing power (coloring uniformity) of the coating.
In order to guarantee that the elements of the seat frame (the tank, etc.) have a sufficient capacitance while the distance between the legs of the rider when the rider sits on the seat is set appropriately (so as not to be too wide), it is preferable that distance between the first side wall and the second side wall in the second region is 12 mm or shorter.
In order to obtain a higher strength with certainty, it is preferable that thickness of each of the first side wall and the second side wall is 2 mm or larger.
In order to guarantee that the elements accommodated in the seat frame (the tank, etc.) have a sufficient capacitance, the frame members may each have a curved portion curved with respect to the vehicle length direction. In this case, the width of the connecting wall may become narrow at the curved portion. By arranging the curved portion to be in the second region (having the H-shaped cross-section), the narrowed portion of the connection wall is easily guaranteed to have a sufficient strength.
As described above, the present invention can suppress the generation of a casting defect which would otherwise occur to a seat frame when being cast using a magnesium alloy or an aluminum alloy. Therefore, the present invention can realize a lightweight seat frame at low cost. A saddle-riding type transporter including the lightweight seat frame according to the present invention provide superb running performance and fuel consumption.
According to the present invention, the generation of a casting defect can be suppressed which would otherwise occur to frame members of a seat frame when being formed of a magnesium alloy or an aluminum alloy by casting.
Other features, elements, processes, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view schematically showing a motorcycle including a seat frame in a preferable embodiment according to the present invention.
FIG. 2 is an isometric view schematically showing a main frame included in the motorcycle shown in FIG. 1 .
FIG. 3 is an exploded isometric view schematically showing a structure of the seat frame and a portion of the motorcycle shown in FIG. 1 above the seat frame.
FIGS. 4A and 4B schematically show the seat frame in a preferable embodiment according to the present invention; FIG. 4A is a cross-sectional view taken along 4A-4A' in FIG. 3 , and FIG. 4B is a cross-sectional view taken along 4B-4B' in FIG. 3 .
FIG. 5 is an isometric view of an attaching section and the vicinity thereof of the seat frame in a preferable embodiment according to the present invention.
FIGS. 6A and 6B are each a side view showing the attaching section and the vicinity thereof of the seat frame in a preferable embodiment according to the present invention; FIG. 6A shows a case where a second region (region having an H-shaped cross-section) is located in the vicinity of the attaching section, and FIG. 6B shows a case where a first region (region having a U-shaped cross-section) is located in the vicinity of the attaching section.
FIG. 7 is a side view schematically showing the seat frame and a main frame connected to the seat frame in a preferable embodiment according to the present invention.
FIGS. 8A and 8B are each a side view showing the attaching section and the vicinity thereof of the seat frame in a preferable embodiment according to the present invention; FIG. 8A shows a case where the first region (region having a U-shaped cross-section) is located in the vicinity of the attaching section, and FIG. 8B shows a case where the second region (region having an H-shaped cross-section) is located in the vicinity of the attaching section.
FIG. 9 is a top view schematically showing the seat frame and the main frame connected to the seat frame in a preferable embodiment according to the present invention.
FIGS. 10A and 10B are each a cross-sectional view taken along line 10A-10A' in FIG. 9 ; FIG. 10A shows a case where the first region (region having a U-shaped cross-section) is located in the vicinity of the attaching section, and FIG. 10B shows a case where the second region (region having an H-shaped cross-section) is located in the vicinity of the attaching section.
FIGS. 11A, 11B and 11C each show the attaching section and the vicinity thereof of the seat frame in a preferable embodiment according to the present invention; FIG. 11A is a side view of a left frame member seen from the inside of the vehicle width direction, FIG. 11B is a side view of the left frame member seen from the outside of a vehicle width direction, and FIG. 11C is a plan view of the left frame member seen from above.
FIG. 12 is an isometric view of the attaching section and the vicinity thereof of the seat frame in a preferable embodiment according to the present invention.
FIG. 13 is a cross-sectional view showing the seat frame in a preferable embodiment according to the present invention.
FIG. 14 is a plan view showing how an inner side wall and an outer side wall of the seat frame each act as a positioning section usable for attaching a seat in a preferable embodiment according to the present invention.
FIG. 15 is an isometric view of the attaching section and the vicinity thereof of the seat frame in a preferable embodiment according to the present invention.
FIG. 16 is a plan view showing an example of a hole provided in the vicinity of the attaching section of the seat frame in a preferable embodiment according to the present invention.
FIGS. 17A and 17B are each a plan view showing an example of a hole provided in the vicinity of the attaching section of the seat frame in a preferable embodiment according to the present invention.
FIG. 18 is a plan view showing an example of a hole provided in the vicinity of the attaching section of the seat frame in a preferable embodiment according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following, a seat frame for a motorcycle will be described as an example, but the present invention is not limited to this and is widely applicable to a seat frame for a saddle-riding type transporter. For example, the present invention is also usable for a snow mobile (SMB), an all terrain vehicle (ATV), a water vehicle or the like.
FIG. 1 shows a motorcycle 200 including a seat frame 100 in this embodiment. The motorcycle 200 includes a fuel tank 101, a main frame 102, the seat frame 100, an internal combustion engine 108, a front wheel 116, and a rear wheel 126. The motorcycle 200 is a saddle-riding type transporter (motorized vehicle) on which a rider may get astraddle.
FIG. 2 is an isometric view showing the main frame 102 in enlargement. The main frame 102 includes a pair of frames 102A and 102B connected to a head pipe 112 which is located in a front portion of the vehicle. The frames 102A and 102B are curved in a central portion of the motorcycle 200 to extend downward. The frames 102A and 102B are connected to each other at ends thereof. The curved portions of the frames 102A and 102B are connected to each other by a connection portion 102C. The connection portion 102C includes a pair of first engageable sections 102a and a pair of second engageable sections 102b for connecting the connection portion 102C to the seat frame 100. In this embodiment, the first engageable sections 102a and the second engageable sections 102b are each a stay having a hole through which a bolt may be inserted. The main frame 102 and the seat frame 100 form a body of the motorcycle 200.
As shown in FIG. 1 , a front fork 114 is rotatably attached to the head pipe 112. At one end of the front fork 114, the front wheel 116 is rotatably supported. To the other end of the front fork 114, a steering handle 110 is fixed.
The fuel tank 101 is attached in the vicinity of a central portion of the motorcycle 200 while being astraddle over the main frame 102 and the seat frame 100. Forward with respect to the fuel tank 101, an air cleaner 128 is provided. The fuel tank 101 is provided with a cap 130 for covering a fuel injection opening (not shown).
The internal combustion engine 108 is supported by the main frame 102 to be located below the fuel tank 101. Forward with respect to the internal combustion engine 108, a radiator 106 is provided. To an exhaust port of the internal combustion engine 108, an exhaust pipe 118 is connected. Although not shown in detail in FIG. 1 , an end of the exhaust pipe 118 is separated into a plurality of portions, which respectively guide exhaust gas from a plurality of cylinders of the internal combustion engine 108. The exhaust pipe 118 pass below the internal combustion engine 108 to be guided rearward along the seat frame 100. The exhaust pipe 118 is separated into two at a position in the vicinity of the seat frame 100, and each of the two separated pipes is connected to a muffler 120. The exhaust pipe 118 and the muffler 120 are supported by the seat frame 100. The seat frame 100 is provided with a pair of footrests 145.
The main frame 102 is connected to a swing arm 122, and the rear wheel 126 is rotatably supported by the swing arm 122. A rotation driving force of the internal combustion engine 108 is transmitted to the rear wheel 126 via a chain 124.
In addition to the above described elements, the motorcycle 200 includes an external cover 134 for covering a bottom portion of the fuel tank 101, a rider seat 136, a rear cover 137, a side cover 138, and a passenger seat 139. These elements are shown with dashed lines in FIG. 1 in order to show the seat frame 100 clearly.
As described above, the main frame 102 and the seat frame 100 form the body of the motorcycle 200, and need to have a high strength in order to support the various structural elements of the motorcycle 200. Especially, the seat frame 100 supports the rider seat 136, the passenger seat 139 and the footrests 145, and so is to receive the body weights of the rider and the passenger.
Hereinafter, with reference to FIGS. 3 , 4A and 4B , a structure of the seat frame (also referred to as a "sub frame" or "rear frame") 100 in this embodiment will be described. FIG. 3 is an exploded isometric view showing the seat frame 100 and a portion of the motorcycle 200 above the seat frame 100. FIG. 3 shows the seat frame 100, the rider seat 136, the side cover 138 and the passenger seat 139. FIGS. 4A and 4B are cross-sectional views respectively taken along lines 4A-4A' and 4B-4B' in FIG. 3 .
As shown in FIG. 3 , the seat frame 100 includes a pair of frame members (seat rails) 10R and 10L formed of a magnesium alloy or an aluminum alloy by casting and a connecting member 20 for connecting the pair of frame members 10R and 10L to each other. The frame members 10R and 10L extend in a vehicle length direction (front-rear direction) A. By contrast, the connecting member 20 extends in a vehicle width direction (left-right direction) B.
In this embodiment, the frame members 10R and 10L and the connecting member 20 are integrally formed by casting (e.g., diecasting). The connecting member 20 may be formed separately from the frame members 10R and 10L and mechanically connected with the frame members 10R and 10L. In the case of being formed separately from the frame members 10R and 10L, the connecting member 20 does not absolutely need to be formed of the same material as that of the frame members 10R and 10L (a magnesium alloy or an aluminum alloy). Nonetheless, it is preferable that the connecting member 20 is formed of the same material as that of the frame members 10R and 10L in order to have a sufficient level of corrosion resistance with certainty.
As shown in FIGS. 4A and 4B , the frame members 10R and 10L each include a first side wall 11, a second side wall 12 located outer with respect to the first side wall 11 in the vehicle width direction B, and a connecting wall (top wall) 13 for connecting the first side wall 11 and the second side wall 12 to each other. Hereinafter, the first side wall 11, which is located relatively inner, will be referred to as an "inner side wall"; and the second side wall 12, which is located relatively outer, will be referred to as an "outer side wall". A bottom end of the inner side wall 11 of one of the frame members, i.e., the frame member 10R, and a bottom end of the inner side wall 11 of the other frame member 10L are connected to each other by the connecting member 20.
As shown in FIG. 3 , the connecting walls 13 each include a first engageable section 13a for attaching the rider seat 136 to the seat frame 100. The rider seat 136 is shaped like a saddle and includes a pair of engageable sections 136a. As shown in FIG. 3 with the dashed lines, the engageable sections 136a of the rider seat 136 are engaged with the first engageable sections 13a of the frame members 10R and 10L, and thus the seat frame 100 and the rider seat 136 are connected to each other.
The first engageable sections 13a of the frame members 10R and 10L, and the engageable sections 136a of the rider seat 136, may have any structure as long as being engageable with each other directly (or via another element) to fix the rider seat 136 to the seat frame 100. In this embodiment, these engageable sections each have a hole. A caulking nut with a female screw is inserted into each hole and is tightened with a bolt, and thus the engageable sections are connected to each other.
The connecting walls 13 each include a second engageable section 13b and a third engageable section 13c for attaching the side cover 138 to the seat frame 100. The side cover 138 includes a pair of first engageable sections 138a, a pair of second engageable sections 138b, and a support frame 138c for fixing the passenger seat 139. As shown in FIG. 3 with the dashed lines, the first engageable sections 138a of the side cover 138 are engaged with the second engageable sections 13b of the frame members 10R and 10L, and the second engageable sections 138b of the side cover 138 are engaged with the third engageable sections 13c of the frame members 10R and 10L. Thus, the seat frame 100 and the side cover 138 are connected to each other. The passenger seat 139 is fixed to the seat frame 100 via the support frame 138c of the side cover 138.
The second engageable sections 13b and the third engageable sections 13c of the frame members 10R and 10L, and the first engageable sections 138a and the second engageable sections 138b of the side cover 138, may have any structure as long as being engageable with each other directly (or via another element) to fix the side cover 138 to the seat frame 100. In this embodiment, these engageable sections each have a hole, and are respectively connected to each other by a bolt and a nut.
As described above, the connecting walls 13 each include the first engageable section 13a, the second engageable section 13b, and the third engageable section 13c for fixing the seats (the rider seat 136 and the passenger seat 139). Hereinafter, the first engageable section 13a, the second engageable section 13b, and the third engageable section 13c of the connecting walls 13 may be collectively referred to as "seat fixing sections".
As shown in FIG. 3 , a front end portion of each of the frame members 10R and 10L (an end closer to the internal combustion engine 108) includes a fourth engageable section 10a and a fifth engageable section 10b as an attaching section for attaching the seat frame 100 to the main frame 102. In this embodiment, the fourth engageable section 10a and the fifth engageable section 10b are each a boss having a hole (through-hole) through which a bolt may be inserted. The fourth engageable sections 10a and the fifth engageable sections 10b of the frame members 10R and 10L are engaged with the first engageable sections 102a and the second engageable sections 102b (see FIG. 2 ) of the main frame 102, and thus the seat frame 100 and the main frame 102 are connected to each other. Hereinafter, each of the fourth engageable sections 10a and the fifth engageable sections 10b of the frame members 10R and 10L may also be referred to as an "attaching section" or "boss").
The seat frame 100 has, for example, the following external size. A width of the connecting member 20 on the internal combustion engine 108 side (i.e., distance between the pair of frame members 10R and 10L) is about 200 mm to 300 mm, and a height of each of the frame members 10R and 10L on the internal combustion engine 108 side is about 80 mm to 160 mm. A length of the seat frame 100 in the vehicle length direction A is about 600 mm to 800 mm.
The frame members 10R and 10L each have a first region R1 and a second region R2 which are different from each other in the cross-sectional structure (structure in a cross-section which is perpendicular to the vehicle length direction A and parallel to the vehicle width direction B). In this embodiment, the second regions R2 are located in the vicinity of the attaching sections 10a and 10b provided in the front end portions of the frame members 10R and 10L, and the first regions R1 are located rearward with respect to the second regions R2. Namely, the second regions R2 are located between the attaching sections 10a and 10b and the first regions R1.
Hereinafter, with reference also to FIG. 5 , a cross-sectional structure of the frame members 10R and 10L in each of the first regions R1 and the second regions R2 will be described. FIG. 5 is an isometric view showing the attaching sections 10a and 10b and the vicinity thereof of the frame member 10L in enlargement. In FIG. 5 , the attaching sections 10a and 10b are shown as bosses having through-holes 10a1 and 10b1 as an example.
As shown in FIGS. 4A and 5 , in the first region R1, a top end of the inner side wall 11 and a top end of the outer side wall 12 are connected to each other by the connecting wall 13. Therefore, in the first region R1, a top portion of each of the frame members 10R and 10L has a U-shaped cross-section.
By contrast, as shown in FIGS. 4B and 5 , in the second region R2, a portion below the top end of the inner side wall 11 and a portion below the top end of the outer side wall 12 are connected to each other by the connecting wall 13. Therefore, in the second region R2, a top portion of each of the frame members 10R and 10L has an H-shaped cross-section.
As described above, in this embodiment, the frame members 10R and 10L of the seat frame 100 have two regions R1 and R2 having different cross-sectional structures. As compared with a U-shaped cross-section, an H-shaped cross-section generates a smaller stress when being twisted and so has a higher strength. Therefore, as compared with conventional seat frame in which the frame members entirely have a U-shaped cross-section, the seat frame 100 having the second region R2 in a part of each of the frame members 10R and 10L has a higher strength. For this reason, the connecting walls 13 do not need to be thick, and so the thickness difference between the connecting walls 13 and the side walls (the inner side walls 11 and the outer side wall 12) can be smaller. This can decrease the difference in the cooling rate at the time of casting between the connecting walls 13 and the side walls, which can suppress the generation of shrinkage cracks or shrinkage porosities.
As can be seen from FIGS. 4B and 5 , in the H-shaped cross-section, the top end of the inner side wall 11 and the top end of the outer side wall 12 protrude more upward than a top surface of the connecting wall 13. Therefore, in the case where the frame members 10R and 10L entirely have the H-shaped cross-section, it is difficult to attach the seats to the frame members 10R and 10L. However, in the seat frame 100 in this embodiment, as shown in FIG. 3 , the seat fixing sections 13a, 13b and 13c for fixing the seats are located in the first regions (having the U-shaped cross-section) R1. Therefore, the seats can be fixed easily. Namely, by causing each of the frame members 10R and 10L to have the two regions R1 and R2 having different cross-sectional structures as in this embodiment, the generation of casting defects can be suppressed without obstructing the fixation of the seats.
In this embodiment, the second region R2 is located in the vicinity of the attaching sections 10a and 10b. This can suppress the generation of casting defects in the vicinity of the attaching sections 10a and 10b with more certainty. The reason for this will be described with reference to FIGS. 6A and 6B .
FIGS. 6A and 6B are side views showing the attaching sections 10a and 10b and the vicinity thereof of the frame member 10L. FIG. 6A shows a case where the second region R2 is located in the vicinity of the attaching sections 10a and 10b. FIG. 6B shows a case where the first region R1 is located in the vicinity of the attaching sections 10a and 10b.
As shown in FIGS. 6A and 6B , the attaching sections 10a and 10b are respectively cylindrical bosses having through-holes 10a1 and 10b1. One of the bosses, i.e., the boss 10a, is provided at a top end of the front end portion of the frame member 10L, and the other boss 10b is provided at a bottom end of the front end portion of the frame member 10L.
In the example shown in FIG. 6A , a central portion of the upper boss 10a and the connecting wall 13 are connected to each other. By contrast, in the example shown in FIG. 6B , a top portion of the upper boss 10a and the connecting wall 13 are connected to each other. As understood from the comparison of FIGS. 6A and 6B, in the example shown in FIG. 6B , pads 9 is generated in the vicinity of the boss 10a, and the thickness is larger in this portion than in the remaining portion of the vicinity of the boss 10a. As can be seen from this, in the case where the first region R1 is located in the vicinity of the attaching sections 10a and 10b, pads is generated depending on the structure or location of the attaching sections 10a and 10b, and the cooling rate at the time of casting is decreased in such a portion. By contrast, in the case where the second region R2 is located in the vicinity of the attaching sections 10a and 10b, such pads can be made smaller. Therefore, the coolability can be improved in the vicinity of the attaching section (in the example of FIG. 6A , the upper boss 10a) and the generation of casting defects can be suppressed with more certainty.
In the case where the second region R2 is located in the vicinity of the attaching sections 10a and 10b, the following effects are also provided. When the rider sits on the seat, as schematically shown in FIG. 7 , a bending stress acts on the seat frame 100 because of the body weight of the rider.
The following occurs in the attaching section 10a and the vicinity thereof. FIG. 8A shows the case where the first region R1 is located in the vicinity of the attaching section 10a. FIG. 8B shows the case where the second region R2 is located in the vicinity of the attaching section 10a. In the case of FIG. 8A , as compared with the case of FIG. 8B , the connecting wall 13 is farther from the central axis of the through-hole 10a1, and so the bending stress acting on the connecting wall 13 is larger. Where the connecting wall 13 is increased in the thickness in order to be against such a larger bending stress, the cooling rate of the connecting wall 13 is decreased, which may generate shrinkage cracks or shrinkage porosities. By contrast, in the case of FIG. 8B , as compared with the case of FIG. 8A , the connecting wall 13 is closer to the central axis of the through-hole 10a1, and so the bending stress acting on the connecting wall 13 can be smaller. Therefore, the connecting wall 13 does not need to be increased in the thickness in order to be against such an excessively large bending stress, and so the generation of casting defects is suppressed.
For attaching the seat frame 100 to the main frame 102, a torsional stress may act on the attaching section 10a and the vicinity thereof. For example, as shown in FIG. 9 , a prescribed clearance is provided between the attaching sections (the fourth engageable sections) 10a of the seat frame 100 and the first engageable sections 102a of the main frame 102 for the purpose of facilitating the positional alignment of the engageable sections. When the seat frame 100 and the main frame 102 are tightened (e.g., by a bolt) in such a state, a torsional stress acts on the attaching sections 10a and the vicinity thereof of the seat frame 100 by the tightening force.
FIGS. 10A and 10B each show a cross-section taken along line 10A-10A' in FIG. 9 . FIG. 10A shows the case where the top portion of each of the frame members 10R and 10L has the U-shaped cross-section in the vicinity of the attaching section 10a (i.e., the case where the first region R1 is located in the vicinity of the attaching section 10a).
FIG. 10B shows the case where the top portion of each of the frame members 10R and 10L has the H-shaped cross-section in the vicinity of the attaching section 10a (i.e., the case where the second region R2 is located in the vicinity of the attaching section 10a).
In the case of FIG. 10A , as compared with the case of FIG. 10B , each connecting wall 13 is farther from the central axis of the through-hole 10a1, and so the torsional rigidity of the frame members 10R and 10L in the attaching sections 10a is higher. Where the torsional rigidity is too high, the stress generated at the time of attaching may become large and destroy the seat frame 100. The torsional rigidity can be reduced and the destruction can be prevented by reducing the thickness of the connecting wall 13. However, in such a case, the connecting wall 13 cannot be against the large bending stress described above with reference to FIG. 8A . By contrast, in the case of FIG. 10B , as compared with the case of FIG. 10A , the connecting wall 13 is closer to the central axis of the through-hole 10a1, and so the torsional rigidity of the frame members 10R and 10L in the attaching sections 10a can be smaller. Therefore, the stress at the time of attaching can be reduced.
In FIGS. 8B and 10B , the connecting wall 13 and the through-hole 10a1 are located at substantially the same level of height, namely, the central axis of the through-hole 10a1 is on an extension line of the connecting wall 13. The relative positional relationship between the connecting wall 13 and the through-hole 10a1 is not limited to this. In the case where the central axis of the through-hole 10a1 is on an extension line of the connecting wall 13, the effect of reducing the bending stress acting on the connecting wall 13 (the bending stress generated around the central axis) is high and the effect of reducing the torsional rigidity in the attaching section 10a and the vicinity thereof is also high.
In order to improve the strength of the seat frame 100, it is preferable that the width of each of the frame members 10R and 10L (width in the vehicle width direction B) is wide. However, the width of each of the frame members 10R and 10L cannot be infinitely wide because of the relationship with the distance between the legs of the rider when the rider sits on the seat and with the capacitance of the elements of the seat frame 100 (the fuel tank 101, etc.). In order to provide a sufficiently high strength under such constraints, it is preferable that the second region R2 extends to a position at least 50 mm away rearward from the central axis of the through-hole 10a1 of the boss 10a as an attaching section. Namely, it is preferable that the distance from the central axis of the through-hole 10a1 to an end of the second region R2 (end opposite to the attaching section 10a) is 50 mm or longer.
Now, with reference also to FIGS. 11A, 11B and 11C , a more preferable structure of the inner side wall 11 and the outer side wall 12 in the second region R2 will be described. FIGS. 11A, 11B and 11C each show the attaching section 10a and the vicinity thereof of the frame member 10L. FIG. 11A is a side view of the frame member 10L seen from the inside in the vehicle width direction B, whereas FIG. 11B is a side view of the frame member 10L seen from the outside in the vehicle width direction B. FIG. 11C is a plan view of the frame member 10L seen from above.
In the second region R2, it is preferable that height h1 from the top surface of the connecting wall 13 to the top end of the inner side wall 11 and height h2 from the top surface of the connecting wall 13 to the top end of the outer side wall 12 increase toward the attaching section 10a as shown in FIGS. 11A and 11B . Namely, it is preferable that the depth of the groove made by the connecting wall 13, the inner side wall 11 and the outer side wall 12 continuously increases toward the attaching section 10a. Owing to such a structure, the stress can be slowly changed in the second region R2 and thus the generation of a stress-concentrated area can be prevented.
In order to further improve the bending strength in a height direction (up-down direction), it is preferable that heights h1 and h2 at an end of the second region R2 on the attaching section 10a side (shown as h1' and h2' in FIGS. 11A and 11B ) are each 6 mm or larger.
In order to guarantee that the elements of the seat frame 100 (the fuel tank 101, etc.) have a sufficient capacitance while the distance between the legs of the rider when the rider sits on the seat is set appropriately (so as not to be too wide), it is preferable that distance sp (see FIG. 11C ) between the inner side wall 11 and the outer side wall 12 in the second region R2 is 12 mm or shorter.
In order to obtain a higher strength with certainty, it is preferable that thickness t1 of the inner side wall 11 and thickness t2 of the outer side wall 12 (see FIG. 11C ) are each 2 mm or larger.
In order to guarantee the elements accommodated in the seat frame 100 (e.g., the fuel tank 101, etc.) have a sufficient capacitance, the frame members 10R and 10L may each have a curved portion curved with respect to the vehicle length direction A (i.e., the portion extending in the vehicle length direction A and protruding in the vehicle width direction B). FIG. 5 shows the frame member 10L having such a curved portion. In the case where the frame members 10R and 10L each have a curved portion, the width of the connecting wall 13 may become narrow at the curved portion as shown in FIG. 5 . By arranging the curved portions to be in the second region R2 (having the H-shaped cross-section), even the narrowed portion of the connection wall 13 is easily guaranteed to have a sufficient strength.
As described above, in this embodiment, since the frame members 10R and 10L each have two regions having different cross-sectional structures (the first region R1 and the second region R2), the seat frame 100 can suppress the generation of casting defects without obstructing the fixation of the seats.
As shown in FIGS. 12 and 13 , each of the frame members 10R and 10L may further include a third region R3, which is different in the cross-sectional structure from the first region R1 and the second region R2. FIG. 12 is an isometric view of the frame member 10L having the third region R3. FIG. 13 is a cross-sectional view of the frame members 10R and 10L having the third region R3. As shown in FIGS. 12 and 13 , in the third region R3, the top end of the inner side wall 11 and a portion below the top end of the outer side wall 12 are connected to each other by the connecting wall 13. Accordingly, in the third region R3, the top portion of the frame member 10L has an h-shaped cross-section.
In the case where the third region R3 is located between the first region R1 and the second region R2 as shown in FIG. 12 , the inner side wall 11 and the outer side wall 12 can act as a positioning section usable for attaching the seat. Specifically, as shown in FIG. 14 , in the third region R3, the inner side wall 11 can act as a positioning section for the vehicle length direction A and the outer side wall 12 can act as a positioning section for the vehicle width direction B. This further facilitates the attachment of the seat.
In the second region R2 and the third region R3, it is preferable that height h1 from the top surface of the connecting wall 13 to the top end of the inner side wall 11 and height h2 from the top surface of the connecting wall 13 to the top end of the outer side wall 12 increase toward the attaching section 10a as shown in FIGS. 11A and 11B. Owing to such a structure, the stress can be slowly changed between the second region R2 and the third region R3 having different cross-sectional structures and thus the generation of a stress-concentrated area can be prevented.
It is preferable that the connecting walls 13 of the frame members 10R and 10L each have a hole in the vicinity of the attaching section 10a. FIG. 15 shows the frame member 10L having a hole 13H in the vicinity of the attaching section 10a. Herein, the hole 13H is a through-hole. Owing to the hole 13H formed in the vicinity of the attaching section 10a, the cooling rate of the portion in the vicinity of the hole 13H is increased. This can suppress the generation of casting defects in this portion with more certainty. Another effect that the seat frame 100 can be more lightweight is also provided.
The hole 13H may be a non-through-hole (hole with a bottom). In the case where the hole 13H is a non-through-hole, the depth of the hole 13H may be entirely constant or may increase toward the attaching section 10a.
In the case where the hole 13H is a through-hole as in this embodiment, the effect of suppressing the generation of casting defects is high. In the case where the hole 13H is a through-hole, the hole 13H can act as a water hole and so the corrosion resistance is improved. Furthermore, the generation of an air pocket is prevented at the time of undercoating or electrodeposition coating. This provides an effect of improving the throwing power (coloring uniformity) of the coating.
FIG. 15 shows the hole 13H having an outer edge contacting the attaching section 10a as an example. The location of the hole 13H is not limited to this. For example, as shown in FIG. 16 , the outer edge of the hole 13H may be slightly distanced from the attaching section 10a. In order to enhance the effect of suppressing the generation of casting defects, it is preferable that at least a part of the hole 13H is located within 3 mm from the attaching section 10a.
The hole 13H is not limited to having a quadrangular shape (square or rectangular) as shown in FIG. 15 or 16 . The shape of the hole 13H may be a circle as shown in FIG. 17A or may be a combination of a quadrangular shape and a part of a circle (herein, semicircle) as shown in FIG. 17B .
There is no specific limitation on the size of the hole 13H. It is preferable that the hole 13H have an area of 6 mm² or larger and 160 mm² or smaller. Where the area of the hole 13H is smaller than 6 mm², the effect of suppressing the generation of casting defects may not be sufficiently provided. Where the area of the hole 13H is larger than 160 mm², it may be difficult to guarantee a sufficient strength of the connecting wall 13. Herein, the "area" of the hole 13H is a cross-sectional area of the hole 13H when seen from above and is an area of a white portion surrounded by the hatched region in FIGS. 16 through 18 .
FIGS. 15 through 17B each show a structure having only one hole 13H in the vicinity of the attaching section 10a. As shown in FIG. 18 , there may be a hole 13H1 in the vicinity of an intersection of the inner side wall 11 and the attaching section 10a and a hole 13H2 in the vicinity of an intersection of the outer side wall 12 and the attaching section 10a. In order to enhance the effect of suppressing the generation of casting defects, it is preferable that at least a part of the hole 13H1 is located within 3 mm from the intersection of the inner side wall 11 and the attaching section 10a. For the same purpose, it is preferable that at least a part of the hole 13H2 is located within 3 mm from the intersection of the outer side wall 12 and the attaching section 10a.
Now, a method for producing the seat frame 100 will be described. The seat frame 100 can be preferably produced by, for example, diecasting. Diecasting, which is a casting method using a die, provides a high size precision and so is suitable to mass production.
For forming the seat frame 100 of a magnesium alloy, it is preferable to use an Mg-Al-Mn type alloy as the magnesium alloy. Especially in order to guarantee the ductility, it is preferable to use an Mg-Al-Mn type alloy containing 3 wt.% or higher and 9 wt.% or lower of Al and 0.1 wt.% or higher and 6.5 wt.% or lower of Mn. For example, AM60B alloy of the ASTM Standards (an Mg-Al-Mn type alloy containing 5.5 to 6.5 wt.% of Al, 0.22 wt.% or lower of Zn, 0.25 to 0.5 wt.% of Mn, 0.1 wt.% or lower of Si, 0.01 wt.% or lower of Cu, 0.002 wt.% or lower of Ni, 0.005 wt.% or lower of Fe, and 0.02 wt.% or lower of other impurities) is preferably usable.
For forming the seat frame 100 of an aluminum alloy, it is preferable to use an Al-Si-Mg type alloy as the aluminum alloy. It is more preferable to use an Al-10Si-lMg alloy.
The seat frame 100 can also be preferably produced by thixo-molding. According to thixo-molding, a metal material in a semi-solid state is injected into a die to be molded. In this specification, even a metal material in a semi-solid state is also referred to as "molten metal" unless otherwise specified. The present invention is preferably applicable to the seat frame 100 produced by a method of injecting a molten metal into a die at a high speed and a high pressure such as diecasting, thixo-molding or the like.
As described above, the present invention can suppress the generation of a casting defect which would otherwise occur to a seat frame when being molded using a magnesium alloy or an aluminum alloy. Therefore, the present invention can realize a lightweight seat frame for a motorcycle at low cost. A motorcycle including the lightweight seat frame according to the present invention provides superb running performance.
The present invention can suppress the generation of a casting defect which would otherwise occur to frame members of a seat frame when being formed of a magnesium alloy or an aluminum alloy by casting. The seat frame according to the present invention can be produced to be lightweight and at low cost, and so is preferably usable for various types of saddle-riding type transporters including motorcycles.
While the present invention has been described with respect to preferred embodiments thereof, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than those specifically described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention that fall within the true spirit and scope of the invention.

Claims

A seat frame for a saddle-riding type transporter, the seat frame comprising a pair of frame members formed of a magnesium alloy or an aluminum alloy by casting;
wherein:
the pair of frame members each include a first side wall, a second side wall located outer with respect to the first side wall in a vehicle width direction, and a connecting wall for connecting the first side wall and the second side wall to each other;

the connecting wall includes a seat fixing section for fixing a seat;

the pair of frame members each include a first region in which a top end of the first side wall and a top end of the second side wall are connected to each other by the connecting wall, and a second region in which a portion below the top end of the first side wall and a portion below the top end of the second side wall are connected to each other by the connecting wall; and

the seat fixing section is located in the first region.
The seat frame of claim 1, wherein:
the pair of frame members each further include a third region in which the top end of the first side wall and a portion below the top end of the second side wall are connected to each other by the connecting wall; and

the third region is located between the first region and the second region.
The seat frame of claim 1 or 2, wherein:
the pair of frame members each include an attaching section in a front portion thereof for attaching the seat frame to a main frame; and

the second region is located in the vicinity of the attaching section.
The seat frame of claim 3, wherein the attaching section includes a boss having a through-hole.
The seat frame of claim 4, wherein the second region extends to a position at least 50 mm away rearward from a central axis of the through-hole.
The seat frame of claim 4 or 5, wherein the central axis of the through-hole is located on an extension line of the connecting wall.
The seat frame of any one of claims 3 through 6,
wherein in the second region, a height from a top surface of the connecting wall to the top end of the first side wall and a height from the top surface of the connecting wall to the top end of the second side wall increase toward the attaching section.
The seat frame of any one of claims 3 through 7,
wherein at an end of the second region on the attaching section side, the height from the top surface of the connecting wall to the top end of the first side wall and the height from the top surface of the connecting wall to the top end of the second side wall are each 6 mm or larger.
The seat frame of any one of claims 3 through 8,
wherein the connecting wall has a hole in the vicinity of the attaching section.
The seat frame of claim 9, wherein the hole is a through-hole.
The seat frame of any one of claims 1 through 10,
wherein in the second region, a distance between the first side wall and the second side wall is 12 mm or shorter.
The seat frame of any one of claims 1 through 11,
wherein the first side wall and the second side wall each have a thickness of 2 mm or larger.
The seat frame of any one of claims 1 through 12,
wherein in the second region, the pair of frame members each include a curved portion curved with respect to a vehicle length direction.
A saddle-riding type transporter, comprising:
a seat; and

the seat frame according to any one of claims 1 through 13 for supporting the seat.